During the process of plating substrates, for example magnetic storage disks used in hard disk drives, substrates may be exposed to a bath including a plating fluid. While the substrates are submerged in the bath, the plating fluid may react with the surfaces of the substrates, resulting in plated substrates. Some plating processes may include the use of a pump to move the plating fluid into a vessel that holds the bath. Filters may be used to filter out particles or gas bubbles.
Some factors may affect the plating process, including the substrate exposure time, the movement of the plating fluid, and the amount/concentration of defect-causing particles or gas bubbles within the bath. For example, the bath may contain plastics introduced by the grinding of gears or the rubbing of retaining bars against the substrates. The gas bubbles or particles may cause substrate plating defects, e.g. substrate pits, substrate bumps, inclusion pits, etc.
The substrates may be mounted on racks including mandrels or rods that may move the substrates in and out of the bath. Each mandrel may rotate so that the substrates mounted on the mandrels also rotate within the bath. At the same time, multiple mandrels may be positioned to form a carousel that rotates within the bath. However, the motion of the carousel disrupts the flow pattern of the plating fluid, which can inhibit uniform plating of the substrates.
In addition, the disruption of the flow pattern by the carousel may create vortexes in the bath. The vortexes may form dead zones where the particles and gas bubbles are trapped rather than captured and removed by the filters. As a result, the amount particles and gas bubbles within the bath may increase, causing additional plating defects.